Year	%
1972	22.28285
1973	24.88372
1974	26.31161
1975	27.26931
1976	29.61034
1977	26.4758
1978	31.78827
1979	30.25339
1980	30.93853
1981	31.2213
1982	35.24038
1983	35.34513
1984	37.81411
1985	37.74156
1986	41.15076
1987	42.02732
1990	42.04013
1999	30.3323
2006	45.20219
2007	60.21903
2008	53.02537
2010	64.37891
2011	69.19838
2014	71.14645
2015	69.35837